Along with development of information technology in society, requirement of higher information transmission speed and, accordingly, shift of the information signals to higher frequency is increasing. In order to deal with the requirements, electrical circuit substrates to be used for electronic products have been required to be highly functional and highly integrated. In order to solve these problems, EPD (Embedded Passive Device Technology) that is a technology for fabricating the electronic devices such as resistors, capacitors and inductors in circuit substrates has drawn attention.
In general, a ceramic dielectric is used for the capacitor to be mounted. In the case of employing the ceramic dielectric in the EPD, inferior post-processibility for boring and cutting of the circuit substrate and inferior adhesion property become problems. Therefore, an organic-inorganic composite dielectric comprising an organic polymer and an inorganic dielectric combined with each other is proposed as a dielectric excellent in the post-processibility and the adhesion property.
The organic-inorganic composite dielectric is a formed body or film produced by dispersing an inorganic dielectric with a high dielectric constant in a polyphenylene oxide resin, an epoxy resin or the like (see Japanese Kokai Publication Hei-02-225358) and such a resin has a low dielectric constant especially in high frequency region, so that it is necessary to add the inorganic dielectric with high dielectric constant as much as possible. However, the polyphenylene oxide resin and the epoxy resin, which have been conventionally used, are inferior in dispersibility of the inorganic dielectric; therefore, the addition amount is limited and the obtained dielectric constant as a composite dielectric has not yet reached to a satisfactory level.